In a vibratory machine or apparatus of the type generally disclosed in U.S. Pat. No. 3,173,664 which issued to the assignee of the present invention, it is desirable for the tub which receives the work load of parts and media, to have a center of pivotation or pivot axis located above and laterally offset with respect to the center of gravity of the work load within the tub. The pivotally supported tub has also been designed to have a high moment of inertia so that changes in the work load did not significantly affect the tuned natural frequency of the tub system. As disclosed in U.S. Pat. No. 3,643,384, which also issued to the assignee of the present invention, it was found desirable to apply the vibratory impulses at the center of percussion of the pivotally supported tub system and in a direction perpendicular to a line connecting the center of pivotation to the center of gravity. As a result, the pivot point will experience only a resultant torque and no linear shock forces.
The location of the center of gravity below the pivot axis, as shown in above U.S. Pat. No. 3,173,664, also provides for a tub which tends to be statically stable and affords the opportunity for the center of percussion to be located in line with the applied electromagnetic forces so that the linear shock loads on the spring beams and the supporting bolts are minimized. On the other hand, if the pivot axis was located below the center of gravity of the vibratory tub system, an increase in the work load undesirably increases the moment of inertia and also increases the instability of the system. The location of the pivot axis below the center of gravity also has an adverse effect on the location of the center of percussion and would require locating the electromagnetic drive above the tub system in order to minimize linear shock forces at the pivot axis.